This invention relates to a semiconductor integrated circuit device and also to a method for making the device. More particularly, the invention relates to a technique which is effective when applied to an interconnection structure and an interconnecting process of LSI having multilayer interconnections.
In recent years, integration of LSI has been in progress. This leads to increased aspect ratios (i.e. the depth of a connection hole/the diameter of the hole) of the connection hole formed on an inter-layer insulating film between a given Al interconnection and a lower conductor layer, semiconductor region or a lower Al interconnection. In order to prevent the breakage of the Al interconnections in the inside of the connection holes, a so-called tungsten plug technique has been utilized wherein a W (tungsten) film is filled in the connection holes.
To fill the W film up in the connection hole, a W film is deposited, according to the CVD method, on the entire surface of an insulating film in which connection holes have been formed. Subsequently, the W film on the insulating film is etched back, thereby leaving the W film only in the connection holes. For the etching back of the W film, a F (fluorine) plasma is used. In order to prevent the underlying insulating film (silicon oxide film) from being etched out with the F plasma, a underlying layer, which is constituted of stacked films including a Ti film and a TiN film, has been formed beneath the W film.
The underlying film constituted of the Ti/TiN stacked films is very resistant to electromigration or stress migration, and has been employed for interconnection of LSI which is fabricated according to the design rule on the order of submicrons. Interconnections having such a stacked structure as of Ti/TiN/Al--Cu/TiN formed in this order and tungsten plug techniques for this are set out, for example,. in LVSI Multi-level Conference Jun. 7-8, 1994, pp. 36-43.